Control of saw-blade tension in band-saw machines



Feb. 19, 1946. H. F. SWENSON 2,395,237

CONTROL OF SAW-BLADE TENSION IN BAND-SAW MACHINES Filed March 12, 1943 2 Sheets-Sheet 1 Feb. l9, 1946. H. F. SWENSON 2,395,237 I BLADE TENSION IN BAND-SAW MACHINES Filed March 12, 1943 CONTROL OF SAW- 2 Sheets-Sheet 2 INVENTOR.

' ens on I Y Y' Patented Feb. 19, 1946 UNITED STATES PATENT orrica CONTROL or SAW-BLADE TEISQSION IN BAND-'SAW MACHINE Harvey 1i. Swenson. Seattle. Wash. Application March 12,1943, Serial No. 478,971

4 Claim.

band passes about two or more wheels of which one said wheel is a power-wheel and the other wheel or wheels ar idler-wheels. For tensioncontrol purposes and looking to a governed expansion of the saw-compass, the usual arrangement is to permit an idler wheel to bemoved directly toward and from the power wheel through the instrumentality of mounting its supporting axle upon a sliding carriage, and perhaps the most generally used control is a jack-screw assembly which is manually governed by the operator and which is objectionable not only from the fact that the operator must needs relyupon a sense of feel to accomplish thedesired degree of tension but also by reason of the continual attention which is necessary in maintaining, or in attempting to maintain, the proper setting. It is highly important that the band be quite taut to preclude the blade from "wandering as the work is fed into the same, and it is to insure this tautnessthat operators, especially onprecision metal cutting, frequently placethe blade under a tension appreciably greater than is actually necessary. One result of such undue tension is to stretch the blade and unnecessarily shorten the life-span, and a further objection lies in the destructive influence upon the wheel journals.

In an efiort to remove this objectionable hu man equation from band-saw operations, attempts have been made to utilize springs for placing the idler-wheel carriage under a yield- .iections which follow from the use of springs, and visualizing hydraulic-namely, fluid pres sure-force as the answer, the present invention may therefore be said to reside in an advanced mechanism essentially hydraulic in nature which permits absolute accuracy in its tension setting and which may be functionally engaged and disengaged to and from the wheel-carriage at will.

The invention, in moreparticularity, consists in the novel construction and in the adaptation and combination of parts hereinafter described and claimed.

In the accompanying drawings:

Figure 1 is an elevational view illustrating a preferred embodiment of my automatic tension- -.control applied to a conventional band-saw machine, the front wall of the latter being partially broken away to permit a full-line showing of various parts.

Fig. 2 is an enlarged fragmentary transverse vertical section on line 22 of Fig. 1 detailing the booster unit of the control mechanism.

Fig. 3 is a similarly enlarged fragmentary elevational View detailing the carriage for the movable idler-wheel of the machine and indicating. in its functional relation therewith, the actuating hydraulic unit which receives its fluid energy from the booster, said hydraulic unit as well as apart of the Wheel-carriage being shown in iongitudinal vertical section. In properly corelating the parts, it should be noted that Fig. 3 indicates its parts in an operating position while the pistons of the energizing booster are shown as being inoperative in Fig. 2.

Fig. 4 i an enlarged fragmentary transverse vertical section on line 4-4 of Fig. l detailing the pressure regulator which I employ.

ing expansion pressure but results have not been particularly satisfactory due principally to two factors, a difliculty in removing and inserting saw-blades in that it becomes necessary to overpower the springs to enable the wheel-carriage to be brought inwardly sufficient to pass the sawblade over the periphery, and an inability to accurately gauge the spring tension due to variation in the expansion characteristic of the metal which changes with ch ging temperature conditions and age.

Being desirous of accomplishing an accurate automatic tension control without the stated ob- Fige-5isarduced scale front elevational view of said regulator; and

Fig. 6 is an enlarged view partly in elevation and partly in longitudinal verticaLsection to detail thetreadle-operated manual control which permits air to be'exhausted from the line for relieving the wheel-carriage of the actuating pressure.

The machine which I have selected for purposes of illustration is one of various models of band-saw machines produced by Continental Machines, of'Minneapolis, Minn, and known as the Doall band-saw. Referring to the drawings, the cabinet for the machine i indicated by the numeral l0 and provides the usual compartments ll and I2 lying above and below a working throat, the saw blade l3 travelling about an idler wheel I4 and a power wheel l5 housed, re-

spectively, in said compartments. An electric motor for driving the powe wheel and which is belt-connected therewith through a transmission I4 is represented at l1. It indicates the work table. Most of the late-model machines are fittea with a flexible hose 20 arranged to direct a pressure jet of air onto the table for ejecting saw-dust, and for supplying pressure air to the hose it is usual to equip the machine with an air pump 2|, mounting the pump in the lower compartment and driving the same from the motor II.

For governing the tension of the saw-blade, the idler wheel is journaled upon the axle 22 supported by a carriage 23 which finds a slide mounting on parallel guides 24 fixedly connected to and extending between a pair of vertically spaced horizontal arms 25-25 of a rigid frame, and for shifting such carriage the procedure heretofore has been to apply a manually-operated Jackscrew assembly with the screw being given a rotary Journal in the frame arm 25 and extending upwardly through the carriage on the median center line of the latter to engage a travelling nut which is fixed to the carriage, the screw having an operating crank.

Referring now to the present invention, and

first describing the structure detailed in Fig. 3 for operating the wheel-carriage, it will be seen that my arrangement provides an open-top oil cylinder 30 which is fixedly secured to said lower arm 25 of the frame and receives a piston 3| packed, preferably, with a cup-leather 3| to assure a non-leak fit. Footing upon the piston is a piston-rod 32 extending upwardly through the open end of the cylinder and at its upper end seating in a thrust-thimble 33 which in turn shoulders against the underside of the carriages upper cross-arm 23'.

34 denotes an oil pipe to the cylinder and which leads from a complementary cylinder 35 (Fig. 2) formed as and constituting the high-pressure side of a booster which includes a low-pressure cylinder 36, the said booster cylinders respectively receiving pistons 31 and 38 coupled for conJoint movement by a piston-rod 40. The booster is shown as providing a return-spring 39 for influencing the low-pressure piston into the indicated inoperative position, but it is found that the spring can be ordinarily dispensed with in that the weight of the carriage exerts sufficient energy through the oil column, in the absence of an expanding pressure upon the lowpressure side of the booster, to return the piston.

As the prime mover for the booster I resort to the pressure of the air delivered from the air pump 2|, and for this purpose preferably employ the hook-up shown in Fig. 1 in which a branch pipe 4| to the low-pressure cylinder 36 ties in with one outlet from a cross 42, the cross being cut into the air line to connect through a pipe 43 with the air pump. Included in this connection is a non-return check 44. The outlet pipe from the cross is indicated at 45 and leads to a pressure regulator 45 from whence the pressure air carries through a pipe 41 to the delivery hose 23. Threaded into the remaining branch outlet from the cross is a pipe 48 which, for blowing the line, leads to a valved body 50. Detailed in Fig. 6, the outlet from this body is normally closed by a spring-pressed valve I, and connecting with the valve spindle for opening the valve is a treadle 52 fulcrumed, as at 53, to the body.

Reverting to the pressure-regulator, it will be seen from an inspection of Fig. 4 that the device is in the nature of a pressure-relief structure having an inlet 54 exposed to the pressure of the pipe 45, an outlet 55 to the pipe 41, and an intermediate valve-seat 55. Registering with the seat is a valve 51 received in a guide 58 and urged into closing relation to the seat by a spring 60, and governing the pressure of the spring is a threadedly mounted control knob 6|. 62 represents a pressure indicator which is made subject to the pressure within the inlet passage 54, and movable in correspondence with this pressure is a pointer 83 for which I provide a dial desirably calibrated in terms of saw-blade thickness for facilitating the proper setting of the pressure-regulator.

- It may be stated that the air pumps customarily provided for band-saw machines have a 15 lb. pressure capacity, and in engineering the booster I have adapted the same such that a prime moving force somewhat below the capacity of the pump will suffice to obtain a pressure intensity meeting the maximum tension requirements of the various saw-blades used on the machine. Many industrial plants, having an available centralized pressure source of air, do not equip their band-saws with individual air pumps, but it will be evident that the present invention is readily adapted to such installations in that the cylinder 30, either directly or through a booster unit according as the pressure conditions may dictate, may be coupled to any suitable source of fluid pressure.

From the foregoing it will be apparent that the piston 3|, responsive to the prevailing static pressure within the 011 column, places the wheelcarriage under the influence of a like pressure, and that the relief valve 51 will remain open during operating periods of the pump and deliver a substantially constant flow of air to the jet nozzle of the delivery hose 2|. When removing or inserting saw-blades over the periphery of the idler wheel, the operator merely steps on the treadle to exhaust the air from the line, having first disengaged the power wheel from the motor by placing the control handle l5 of the transmission in neutral position. With both hands being thus free, and. permitting a controlled dampening of the pressure-responsive rise of the idler wheel, the invention is of especial value when replacing saw-blades. The idler-wheel will of course be held subject to the pressure at which the regulator is set even during periods when the motor is not running as the air is then trapped between the check valve 44 and the relief valve 51.

While having described a particular embodiment specifically applied to One design of bandsaw machine, modifications within the spirit of the disclosure might be resorted to and may, in some instances, be necessary in adapting the invention to other-type ,machines. I accordingly intend that no limitations be implied and that the hereto annexed claims be read with only such restrictions as are expressly introduced thereto in distinguishing from prior knowledge in the art of saw-blade tension controls.

What I claim is:

1. In combination with the blade-carrying revoluble power and idler drums of a band-saw machine, and with a slide carriage providing the rotary mounting for the idler drum and .by oppositely directed sliding movements increasing and decreasing the tension of a saw-blade applied over the drums: a hydraulic jack operatively' engaging the carriage and by its exerted force acting to slide the carriage in a direction increasing the tension of the blade; an air pump having a pressure capacity less than the pressure required to be exerted by the Jack in placing the saw blade under working tension; an air conduit fed from the pump and terminating in a delivery nozzle arranged and adapted to direct its exhaust jet upon the saw-cut of the material being sawed and thus keep the saw-cut free of accumulating dust; an adjustable pressure-regulating relief valve introduced in the air conduit and delivering its escape air to the delivery nozzle; a source of power common to both the power drum and the air pump functional to drive the two in unison or the air pump independently while being inactive to the power drum; a booster; a branch connection leading from the air conduit to the low-pressure side of the booster from a point between the air pump and the relief valve; and hydraulic connection from the high-pressure side of the booster to the jack.

2. In combination with the blade-carrying revoluble power and idler drumsof a band-saw machine, and with a slide carriage providing the rotary mounting for the idler drum and by oppositely directed sliding movements increasing and decreasing the tension of a saw-blade applied over' the drums: a hydraulic jack operathe air pump independently of the power drum; a booster; a branch connection to the low-pressure side of the booster leading from the air conduit at a point intermediate the relief and check valves; hydraulic connection from the high-pressure. side of the booster to the Jack; a second branch connection also leading from the air conduit at a point intermediate the relief and check 1 valves and terminating in an exhaust opening; a

tively engaging the carriage and by its exerted force acting to slide the carriage in a direction increasing the tension of the blade; an air pump having a pressure capacity less than the pressure required to be exerted by the jack in placing the saw blade under working tension; an air conduit fed from the pump, fitted with a non-return check, and terminating in a delivery nozzle arranged and adapted to direct its exhaust jet upon the saw-cut of the material being sawed and thus keep the saw-cut free of accumulating dust; an adjustable pressure-regulating relief valve introduced in the air conduit between the check valve and the delivery nozzle and delivering its escape air to the delivery nozzle; a power source common to the power drum and to the air pump arranged to drive the two in unison orv to operate spring-closing valve normally closing said exhaust opening; and a treadle for opening the lastnamed valve in opposition to the spring for exhausting air from the conduit to substantially relieve the pressure upon the booster.

3. In combination with the blade-carrying revoluble drums of a band-saw machine, and with a shiftable carriage providing the rotary mounting for one of said drums and by shifting movements in opposite directions respectively increasing and decreasing the tension of a sawblade applied over the drums: a jack adapted to operate by fluid pressure and operatively engaging the carriage to cause the latter, by the exerted force of the jack, to be influenced in a direction increasing the tension of the blade; an air pump; an air conduit fed from the pump and terminating in a delivery nozzle disposed to play its delivered jet upon the material being sawed for ridding the latter of accumulating dust; a pressure-governing relief valve introduced in said air conduit delivering its escape air to the delivery nozzle; and operative interconnection from the air conduit to the jack making the jack subject to the pressure of the pumped air as the latter is governed by the relief valve.

4. Structure according to claim 3 having a. source 0f power common to and operating both the air pump and the saw-blade of the machine, and means for causing said power source to per form both said ofiices in unison or to operate the air pump independently of the operation of the saw-blade.

HARVEY F. SWENSON. 

